The invention relates to a control system for a loading crane provided with a control site, the control system consisting of a control site for a crane operator, a directional control valve positioned external to the control site and arranged to control a hydraulic system of the crane to provide different operations of the crane, and control means influencing actuator spindles of the directional control valve for the control of the directional control valve from the control site of the crane, whereby the control means are constituted by a mechanical rod-driven control lever system.
Such control systems are well-known at present in connection with timber cranes or bulk cranes, for instance. A basic control system of the prior art consists in that a directional control valve positioned outside a control cabin is controlled by means of wires. Control levers are then positioned either at both sides of the control site or at that side which faces the crane, and in a side door turning outwards. When an actuator spindle is controlled by wires, there is, however, always clearance and friction force inside a wire, which impair the control properties. In winter conditions, water may accumulate between the wire and a protecting tube, and frozen water makes the wire get stuck. Moreover, freezing may occur during a control movement and a stuck control lever may then cause a dangerous situation. In addition, the actuator spindles require special fasteners at the ends of the wires.
As a second example of the prior art technique may be mentioned a control system in which a directional control valve is positioned under the operator""s seat. In this control system, control levers are articulated directly with the ends of actuator spindles. At a control site where the directional control valve is positioned under the operator""s seat, problems with noise, heat and odour arise, caused by hot and pressurized hydraulic oil. In a control system of this kind, a movement of a control lever in relation to a movement of an actuator spindle is difficult to adjust so as to suit a movement of a hand. Other drawbacks are caused by hydraulic hoses of the directional control valve being led to actuator connections from the control cabin and by maintenance and adjusting steps, which are difficult to perform for a control valve positioned indoors.
As a third example may be mentioned electro-hydraulic pilot operation of a directional control valve. The valve may then be positioned freely with respect to a control site. A problem is, however, the complicatedness and the high price of the system.
As a fourth example of the prior art technique may be mentioned the control device disclosed in U.S. Pat. No. 4,140,200. Drawbacks of the control device are, however, a relatively complicated structure and an incomplete location and position of a directional control valve.
The object of the invention is to provide a control system by which the drawbacks of the prior art can be eliminated. This has been achieved by means of the control system of the invention, which is characterized in that the directional control valve is positioned external the control site in such a way that the actuator spindles are in a substantially horizontal position.
In comparison to the previously known systems, the invention has for instance the advantage that the amount of hydraulic hoses is smaller than in a model having a directional control valve positioned inside a control cabin, for instance. Easy maintenance and adjusting steps are also a remarkable advantage. A directional control valve mounted outdoors does not cause any noise, heat or odour problems in the control cabin. The control properties provided by mechanical levers are more accurate and more sensitive than those provided by wire control. Winter conditions do not have any detrimental influence on the operation of the mechanics. The directional control valve does not require any special fastenings for actuator spindles, but a standard directional control valve can be used. A movement of control levers in relation to a movement of an actuator spindle is easy to adjust by changing pivot points, by which measure a suitable movement of the control lever is provided. Advantage arises also from the fact that, in the invention, connecting rods of the control levers can be positioned for instance at the sides of the control cabin and connecting rods of pedals close to the floor of the control cabin. By this arrangement, more space is achieved and for instance a heating device of the control cabin can be positioned in this space. In addition, folding control levers provide security, because the levers folding by means of a link make it easier to leave and to enter the control site and also increase the operator""s safety at work by preventing the lever from being moved by the body by mistake. Still an advantage of the invention arises from its simplicity and relatively low costs.